According to the state of the art, a ruptured anterior cruciate ligament is replaced e.g. by a graft, such as e.g. a patellar tendon graft comprising two terminal bone blocks, a hamstring tendon graft (semitendinosus tendon, possibly combined with gracilis tendon), usually being folded and stitched in the end region, i.e. not comprising terminal bone blocks, or a quadriceps tendon graft, which is usually harvested with one terminal bone block. The named grafts are usually autografts but may also be donor grafts (allografts). Donor grafts may also be made of achilles tendons. It is further proposed to use synthetic ribbons (herein called “artificial grafts”) and suitably treated tendon material of slaughtered animals (xenografts), e.g. pigs. The named autografts and allografts may furthermore be reinforced with synthetic material and be combined with bone grafts or synthetic bone substitutes
End regions of all the named grafts (autografts, allografts, xenografts and artificial grafts) need to be fastened in tibia and femur for which purpose a tunnel or a blind bore is provided in either one of the two bones. The blind bore originates from the articular surface and ends inside the bone. The tunnel has a first mouth situated in the articular surface and a second mouth which is not situated in the articular surface, wherein the first mouth and adjoining tunnel portion may have a larger cross section than the second mouth and adjoining tunnel portion. For fastening the graft in the provided opening a plurality of fastener types is known.
A tunnel allows fastening at the inner bone wall of the tunnel (inner fixation) and/or in the vicinity of the second tunnel mouth (outer fixation), a blind opening allows inner fixation only. According to the state of the art inner fixation in a bone opening is effected e.g. with the aid of an interference screw, which is screwed into the opening when the graft is positioned therein; with the aid of a non-threaded, mechanically expandable or non-expandable press-fit element, which is forced without rotation into the opening when the graft is positioned therein or together with the graft; or with the aid of a cross pin which is implanted at an angle to the axis of the opening and engages e.g. a folded end of the graft or a suture loop attached to the graft end. In blind openings inner fixation can also be effected with the aid of a bone screw comprising a head section to which the graft is fixed (hook screw) and which is screwed into the bottom of the blind opening. Inner fixation in a tunnel is usually completed by closing the second tunnel mouth with a bone plug or similar prosthetic element. Various devices and methods for inner fixation are described e.g. in the publications U.S. Pat. Nos. 5,454,811 and 6,099,530 (both to Smith & Nephew), EP-0317406 (Laboureau), or US-2009/222090 (Mayr).
Outer fixation (fixation in the area of a second tunnel mouth not situated in the articular surface) according to the state of the art is effected e.g. with the aid of a button through which the folded graft or a suture loop attached to a graft end is threaded and which is larger than the cross section of the second mouth, or with the aid of a bone screw or similar anchor element which holds the graft or suture ends attached thereto and is screwed or impacted into the bone in the vicinity of the second tunnel mouth. Such outer fixation is also proposed for reinforcing an inner fixation inside the tunnel.
For an inner fixation in a bone tunnel or blind opening with the aid of a fastener such as an interference screw or a press-fit element, the graft or an end portion of the graft respectively is pressed against one side of the opening, while the fastener occupies the other side of the opening. This so called extra-graft fixation is mainly used for one-strand grafts and for grafts comprising a terminal bone block but may also be used for multi-strand grafts. For grafts comprising two strands by e.g. being folded over, the fastener may also be positioned between the two strands separating them from each other, wherein the separated strands are pressed against opposite walls of the bone opening. Such fixation is called intra-graft fixation. Intra-graft fixation is also used for grafts of four or more than four strands, wherein the strands of the graft are pressed against the wall of the bone opening, preferably substantially regularly spaced around the fastener and wherein, between neighboring strands the fastener may or may not be in contact with the bone wall of the opening. Intra-graft fixation is proposed in particular for the graft end at which the strand or strands are folded.
The publication WO 2006/023661 (Scandious Biomedical) discloses a large number of known methods of ACL-fixation, in particular intra-graft fixation with the aid of press-fit fasteners which are additionally secured in the bone tunnel or blind bore.
The quality of most inner graft fixations is in particular dependent on the interface between the graft and the fastener on the one hand and between the graft and the wall of the opening on the other hand, but in most cases it is also dependent on the interface between the fastener and the wall of the opening, wherein good primary stability is desired at all the named interfaces and good long-term stability in particular at the interface between graft and bone tissue (good integration of the graft in the natural tissue by natural tissue growth after the fixation operation). The fixation quality is found to be further depending on the fixation location in the opening, wherein fixation as close to the articular surface seems to be advantageous. For shortening convalescence, good primary stability is desired, for good long-term stability, bone growth in the opening. For allowing a maximum of bone growth in the opening, bioresorbable interference screws and press-fit elements are proposed. Furthermore, it is important that the fastener causes as little damage as possible to the graft neither when being implanted nor later on, and that the graft causes as little widening or other damage as possible to the mouth of the opening, in particular for the case in which this mouth is situated in an articular surface.
The most common failures of known soft tissue fixation methods are caused by graft or tissue damage through the threads of interference screws which can lead to graft or tissue rupture, graft or tissue slippage due to relaxation of a corresponding press fit, or fastener migration on first loading e.g. due to compression of bone tissue in response to anchoring elements such as e.g. barbs, which may lead to loss of tension in the graft or soft tissue.
Known fixation of ligaments other than the anterior cruciate ligament (graft or prosthetic element, or re-attachment of natural ligament), of tendons (graft or prosthetic element, or re-attachment of natural tendon), or of other mainly soft tissues (graft or prosthetic element, or repair) in a bone opening provided for the fixation, with the aid of a fastener are based on the same principles as the above shortly described known fixations used for fastening ACL-grafts in openings provided in tibia and femur. Such fixations are e.g. used in surgical procedures regarding the human foot or ankle, such as e.g. lateral ankle reconstruction, FDL tendon transfer (flexor digitorum longus), FHL tendon transfer (flexor hallucius longus), or flexor to tendon transfer (second toe); surgical procedures regarding the human hand such as e.g. ligament reconstruction tendon interposition, scapholunate ligament reconstruction, collateral ligament reconstruction, or UCL repair (ulnar collateral ligament) of the thumb (also known as “gamekeeper's thumb”); surgical procedures regarding the human elbow such as e.g. UCL repair (ulnar collateral ligament), or distal biceps tendon repair; or surgical procedures regarding the human shoulder such as e.g. proximal biceps tendon repair. A further example is the repair of torn or damaged cranial cruciate ligaments (CCL) in stifle joints of dogs in particular but also of e.g. cats. The CCL is the most commonly damaged stifle ligament in dogs and the named repair is e.g. carried out using nylon bands which are passed around the fabella bone in the back of the femur and are fixed in a bore provided in the front part of the tibia. The same as known fixation methods, the fixation according to the invention is suitable for all the named applications.